Such transmission is usually effected by coupling to the compass shaft an electromagnetic device of the synchro-transmitter type generating a triad of alternating voltages which, when applied to synchro receivers, drive their shafts and associated followers to repeat the position of the compass shaft, possibly with a given step-up ratio.
A drawback of this system consists in the fact that, when the repeaters are numerous, it is necessary to employ a synchro transmitter of considerable dimensions, which is expensive and cumbersome and, above all, presents a strong inertia which retards the response of the servo system. Another drawback is that, when the transmitter has been correctly designed for the contemplated number of followers, it is not possible subsequently to add other followers without giving rise to overloads. A particularly serious drawback of the system consists in the existence of a coupling between the master compass and the followers and among the various loads themselves. Therefore the accidental mechanical blocking of a repeater impairs the follower system of the master compass itself and puts all the other repeaters out of service.